The fast development of the fluorescent microscopy techniques over the last years has made it possible to visualize many biological processes. Among the most important tools used both in biomedical tests and in scientific research are fluorescent dyes allowing to observe target molecules and media in a real-time mode.
Various fluorescent dyes have been used in scientific research for a long time, however the necessity of developing novel fluorescent stain reagents has arisen with the appearance of fluorescent microscopy.
The use of living systems imposed many additional restrictions on the structure of such markers. These compounds must be hydrophilic enough (to exclude non-specific hydrophobic interactions), their absorbance and emission spectra have to lie in visible or even more red region (to reduce phototoxicity and background autofluorescence), and the molecular weight has to be as low as possible (to minimize the influence on labeled biomolecules).
These criteria have significantly limited the range of dyes used, and also narrowed the areas of their application.
This stimulated researchers to develop new specific compounds, which lack such limitations.
Thus, the new dyes with different structures for use in cell biology were created—derivatives of coumarin, rhodamine, carbopyronine and oxazine, available for example from ATTO-TEC [Catalogue 2009/2010 p. 16]. The dyes from Alexa trademark have similar properties. These compounds have high photostability, but their molecular mass is big enough, which limits their application.
The dyes with dipyrrilmethene structure have the structure, similar to the proposed invention [A. Schmitt, B. Hinkeldey, M. Wild, G. Jung, J. Fluoresc., 19, 755 (2009)], [K. Tram, H. Yan, H. A. Jenkins, S. Vassiliev, D. Bruce, Dyes and Pigments 82(3), 392 (2009)]:

with fluoroborylic group in the chromophore nucleus.
Another structural analogue is a dye with structural formula:

(Z)-4-((1-(difluoroboryl)-1H-pyrrol-2-yl)methylene)-1H-imidazole-5(4H)-one, developed by Burgess group [L. Wu, K. Burgess, J. Am. Chem. Soc., 130(12), 4089 (2008)], also containing fluoroborylic group in the chromophore nucleus.
However the above mentioned dyes are rather expensive and synthetically difficult to obtain. This is why they are expensive at the moment.
The chromophore of the Green Fluorescent Protein family (GFP, natural protein from Aequorea victoria jellyfish (avGFP)), is close to the structure of proposed fluorescent dye:

This chromophore is responsible for fluorescence in these proteins after irradiation with light of proper wavelength, but it is not fluorescent in the solution itself, if obtained by chemical synthesis or extracted from the protein. The change in its properties is due to the interaction between two or more amino acid residues, after autocatalytic formation of the chromophore, and their protein surrounding. [J. L. Schwartz, G. H. Petterson, Science, 300, 87 (2003)], [D. M. Chudakov, M. V. Matz, S. Lukyanov, K. A. Lukyanov, Physiol Rev., 90(3), 1103 (2010)].
The artificially synthesized GFP chromophore has the structure, closest to the proposed invention:

(Z)-4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazole-5(4H)-one and its fluorinated derivatives. These compounds do not show any fluorescent properties in solution, but gain them only after binding to the target molecule, which locks chromophore conformationally due to complex space interactions, and therefore ensures the fluorescence [J. S. Paige, K. Y. Wu, S. R. Jaffrey, Science, 333, 642 (2011)]. These properties allow the application of this chromophore in limited list of specific tasks, only when the desired fixation of chromophore by target molecule takes place.
The variety of applied tasks, demanding the use of fluorescent dyes, requires search and development of very diverse compounds, different in the color of fluorescence and absorbance region, hydrophobic/hydrophilic properties, and with different substituents, ensuring their binding to certain targets.
The hypothesis that chemical compounds with the structure similar to GFP chromophore might become useful as low-weight fluorescent dyes, was at the basis of the proposed invention.
However until now there was no evidence of successful use of the GFP chromophore analogues in this role, as it is seen from the sources, cited above.